Wavelength multiplexers and wavelength demultiplexers are used in fiber-optic communications to increase the transmission capacity. With them, the modulated radiation from a plurality of light sources of various wavelengths is simultaneously transmitted through one optical fiber. To join and separate the various wavelength channels with as little loss as possible, it is known to provide a multiplexer and a demultiplexer, which operate with either diffraction gratings or interference filters, at the beginning and end of the transmission segment. A particularly sturdy and compact design is attainable if the space between the diffraction grating or interference filters and the light-conducting fibers for delivering and carrying away the radiation comprises a compact supporting block of transparent material.
Such multiplexers or demultiplexers having diffraction gratings are known, for instance from European patent application Nos. 0 067 972 and 0 093 396. There, coupling faces are provided on the transparent supporting block, where the light-conducting fibers can be coupled in or cemented. It is readily appreciated that the light-conducting fibers must be placed very precisely on the coupling faces. For a coupling face to which many light-conducting fibers must be attached, this involves considerable effort for adjustment, and hence is very expensive.